Relaxed, low-defect SGOI for strained Si CMOS applications

ABSTRACT

Thermal mixing methods of forming a substantially relaxed and low-defect SGOI substrate material are provided. The methods include a patterning step which is used to form a structure containing at least SiGe islands formed atop a Ge resistant diffusion barrier layer. Patterning of the SiGe layer into islands changes the local forces acting at each of the island edges in such a way so that the relaxation force is greater than the forces that oppose relaxation. The absence of restoring forces at the edges of the patterned layers allows the final SiGe film to relax further than it would if the film was continuous.

FIELD OF THE INVENTION

The present invention relates to a method of fabricating a semiconductorsubstrate material, and more particularly to a method of fabricating asubstantially relaxed, low-defect SiGe-on-insulator (SGOI) substratematerial. The present invention also relates to a SGOI substratematerial having the above-mentioned properties as well as structuresthat include at least the inventive SGOI substrate material.

BACKGROUND OF THE INVENTION

In the semiconductor industry, there has been a high-level of activityusing strained Si-based heterostructures to achieve high carriermobility structures for complementary metal oxide semiconductor (CMOS)applications. Traditionally, to boast performance of NFET and PFETdevices, the prior art method to implement this has been to growstrained layers on thick (on the order of from about 1 to about 5micrometers) relaxed SiGe buffer layers.

Despite the high channel electron mobilities reported for prior artheterostructures; the use of thick SiGe buffer layers has severalnoticeable disadvantages associated therewith. First, thick SiGe bufferlayers are not typically easy to integrate with existing Si-based CMOStechnology. Second, the defect density, including threading dislocations(TDs) and misfit dislocations, are from about 10⁶ to about 10⁸defects/cm² which are still too high for realistic VLSI (very largescale integration) applications. Thirdly, the nature of the prior artstructures precludes selective growth of the SiGe buffer layer so thatcircuits employing devices with strained Si, unstrained Si and SiGematerials are difficult, and in some instances, nearly impossible tointegrate.

In order to produce relaxed SiGe material on a Si substrate, prior artmethods typically grow a uniform, graded or stepped, SiGe layer tobeyond the metastable critical thickness (i.e., the thickness beyondwhich dislocations form to relieve stress) and allow misfit dislocationsto form, with the associated threading dislocations, through the SiGebuffer layer. Various buffer structures have been used in an attempt toincrease the length of the misfit dislocation section in the structuresand thereby to decrease the TD density.

When a typical prior art metastable strained SiGe layer is annealed at asufficiently high temperature, misfit dislocations will form and growthereby relieving the total strain on the film. In other words, theinitial elastic strain of the film is relieved by the onset of plasticdeformation of the crystal lattice. For the case of prior art metastablestrained SiGe grown on SOI substrates, experiments have shown that undermost annealing/oxidation conditions, the formation of misfitdislocations occurs early in the annealing history for temperaturesgreater than ˜700° C. Many of these defects are then either consumed orannihilated during the high-temperature annealing of the structure,however, the surface topography of the original misfit array persistsduring oxidation.

Furthermore, prior art methods of fabricating SGOI substrate materialsby thermal diffusion do not completely relax the SiGe alloy layer.Instead, the final SiGe lattice expands only to some fraction of theequilibrium value because for any given small value of SiGe film tryingto relax during oxidation, there are adjacent volumes on all sides whichexert a force opposing that of relaxation. For example, it has beenobserved that when one uses the prior art thermal mixing approach toform SGOI substrate materials, under certain conditions the relaxationof the final SiGe alloy saturates at a value between 40 and 70% for aparticular SOI starting wafer and an initial SiGe alloy layer.

This saturation suggests that an equilibrium condition is reachedbetween the strain-relieving mechanisms and the elastic energy thatpersists within the partially relaxed, compressively strained SGOImaterial. In order for a compressively strained layer to completelyrelax elastically (without defect formation), the lateral (i.e.,parallel to the substrate surface) dimensions of the film must, in someway, increase. To date, the prior art does not provide any means ofincreasing the lateral dimensions of the SiGe alloy film such that theforce of relaxation is greater than the forces opposing relaxation.

In view of the problems mentioned above with prior art processes offabricating a substantially relaxed SGOI substrate material, there is acontinued need for providing a new and improved method that allows forformation of a substantially relaxed, single crystal SiGe buffer layerfor a SOI substrate. The terms “substantially relaxed” or “highlyrelaxed” denote a SGOI substrate wherein the final SiGe alloy is fromabout 50 to about 100% relaxed. Moreover, 100% relaxation denotes a SiGelayer having a (unstrained) diamond-cubic lattice with a latticeconstant that is determined by the Ge fraction and which is the same inall three principal lattice directions.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a method offabricating a thin, high-quality SGOI substrate material.

Another object of the present invention is to provide a method offabricating a thin, high-quality SGOI substrate material that has asubstantially high degree of relaxation associated therewith (50% orgreater).

A further object of the present invention is to provide a method offabricating a thin, high-quality SGOI substrate material that hassubstantially little or no surface artifacts, i.e., defects, associatedtherewith.

A yet further object of the present invention is to provide a method offabricating a thin, high-quality SGOI substrate material that has asignificantly lower density of crystal defects associated therewith.

An even further object of the present invention is to provide a methodof fabricating a thin, high-quality SGOI substrate material whichutilizes processing steps that are compatible with complementary metaloxide semiconductor (CMOS) processing steps.

An additional object of the present invention is to provide a method offabricating a thin, high-quality, substantially relaxed SGOI substratematerial which can be used as a lattice mismatch template, i.e.,substrate, in forming strained Si layers.

A yet additional object of the present invention is to provide strainedSi/substantially relaxed SGOI structures that have high carrier mobilitywhich are useful in high-performance CMOS applications.

These and other objects and advantages are achieved in the presentinvention by utilizing a method wherein a patterning step is used toform a structure containing islands of single-crystal Si and strainedSiGe alloy or islands of a partially relaxed SiGe layer atop a Gediffusion barrier layer. Patterning of the Si and SiGe layers intoislands changes the local forces acting at each of the island edges insuch a way so that the relaxation force is greater than the forces thatoppose relaxation. The absence of restoring forces at the edges of thepatterned layers allows the final SiGe film to relax further than itwould if the film was continuous.

The Ge diffusion barrier layer can serve as a viscous medium upon whichlateral motion of the film island can occur, but only if the lengthscale of the island is small enough. How small is “small enough” willdepend on the thickness of the relaxing film, the integrated lateralstress acting at the interface and the mechanical properties of thematerial. The temperature at which lateral expansion of the SiGe islandcan occur is determined by the visco-elastic properties of the buried Gebarrier layer. Namely, the temperature at which the Ge diffusionresistant barrier layer behaves viscously (it flows). This can becontrolled by introducing dopants into the Ge barrier layer byion-implantation.

Implantation of boron into the Ge barrier layer, for example, could beused to lower the temperature at which strain relaxation of the islandstakes place.

The concept of enhanced relaxation of patterned islands could also beextended to high-temperature, in-situ selective growth of SiGe alloylayers directly on Si islands formed by patterning of a (initially)continuous, thin Si-on-insulator layer. The in-situ relaxed SiGe islandscan then serve as lattice templates for selective Si growth that willresult in tensile strain in the Si layer. A selective epitaxial Sigrowth process could also be used to grow the strained silicon layeronto the relaxed SiGe islands.

One method of the present invention employed in forming thesubstantially relaxed, low defect SGOI substrate material includes thesteps of:

forming a Si_(x)Ge_(1-x) layer, wherein x=0 or a number less than 1, ona surface of a first single crystal Si layer, said first single crystalSi layer has an interface with an underlying barrier layer that isresistant to Ge diffusion;

patterning said Si_(x)Ge_(1-x) layer and said first single crystal Silayer to provide a patterned structure; and

heating said patterned structure at a temperature which permitsrelaxation of strain within the patterned layers and subsequentinterdiffusion of Ge throughout the patterned first single crystal Silayer and the patterned Si_(x)Ge_(1-x), layer to form a substantiallyrelaxed, single crystal SiGe layer atop a portion of the barrier layer.

In another method of the present invention, the following steps areemployed:

forming a Si_(x)Ge_(1-x) layer, wherein x=0 or a number less than 1, ona surface of a first single crystal Si layer, said first single crystalSi layer has an interface with an underlying barrier layer that isresistant to Ge diffusion;

first heating said layers at a temperature which permits interdiffusionof Ge throughout the first single crystal Si layer and theSi_(x)Ge_(1-x) layer to form either a partially relaxed orfully-strained, single crystal SiGe layer atop the barrier layer;

patterning the single crystal SiGe layer; and

second heating the single crystal SiGe layer at a temperature whichpermits complete relaxation of the single crystal SiGe layer to form asubstantially relaxed, single crystal SiGe layer atop a portion of thebarrier layer.

A yet further method of the present invention employed in forming thesubstantially relaxed, low defect SGOI substrate material includes thesteps of:

patterning a first single crystal Si layer into a predeterminedgeometric shape; and

selectively growing an epitaxial SiGe layer about said geometric shapeat a temperature which allows in-situ relaxation of said SiGe layerthereby forming a substantially relaxed SiGe region.

In the inventive methods mentioned above, the geometric shape of thepatterned layer is typically a square or rectangle. The patterningserves to change the local forces acting at each of the island edges insuch a way so that the relaxation force is greater than the forces thatoppose relaxation. The absence of restoring forces at the edges of thepatterned layers allows the final SiGe film to relax further than itwould if the film was continuous. In addition to the enhanced relaxationof the SiGe layer, the final defect density is reduced because theislands are allowed to relax elastically (by lateral expansion on theoxide layer), rather than plastically (by introducing strain-relievingdefects).

It is noted that the substantially relaxed, single crystal SiGe layerformed by either the above embodiments of the present invention iscomprised of a homogeneous mixture of the Si_(x)Ge_(1-x) layer as wellas the first single crystal Si layer. Moreover, the substantiallyrelaxed, single crystal SiGe layer has minimized surface defects and areduced density of crystal defects.

Following the above processing steps, a strained Si layer may beselectively grown epitaxially atop the substantially relaxed, singlecrystal SiGe layer to form a strained-Si/substantially relaxedSiGe-containing heterostructure that can be used in a variety ofhigh-performance CMOS applications.

In some applications of the present invention, the first single crystalSi layer and the barrier layer are components of a silicon-on-insulator(SOI) substrate. In other applications, the barrier layer is formed atopa surface of a semiconductor substrate, and thereafter the first singlecrystal Si layer is formed atop the barrier layer. The latter substratematerial is a non-SOI substrate.

In another application of the present experiment, the first singlecrystal Si layer is a very thin layer having a thickness of about 50 nmor less. The use of a thin starting single crystal layer is useful inminimizing the amount of oxidation required to form the final SGOIthickness and Ge concentration. This is useful in situations whereoxidation of the exposed sidewalls of the patterned islands must beminimized.

The present methods also contemplate the use of Ge barrier layers thatare unpatterned (i.e., barrier layers that are continuous) or patterned(i.e., discrete and isolated barrier regions or islands which aresurrounded by semiconductor material).

In yet another application of the present invention, a Si cap layer isformed atop the Si_(x)Ge_(1-x) alloy layer prior to heating thestructure. This embodiment of the present invention providesthermodynamically stable (in terms of preventing defect production)thin, substantially relaxed SiGe-on-insulator, SGOI, substratematerials. It is noted that the term “thin” when used in conjunctionwith the high-quality, substantially relaxed SiGe-on-insulator substratematerial, denotes that the homogenized SiGe layer formed via theinventive methods has a thickness of about 2000 nm or less, with athickness of from about 10 to about 200 nm being more highly preferred.

Another aspect of the present invention relates to the SiGe-on-insulatorsubstrate material that is formed utilizing the above-mentioned methods.Specifically, the inventive substrate material comprises a Si-containingsubstrate; an insulating region that is resistant to Ge diffusionpresent atop the Si-containing substrate; and a substantially relaxedSiGe layer present atop the insulating region, wherein the substantiallyrelaxed SiGe layer has a thickness of about 2000 nm or less, a measuredrelaxation value of about 50% or greater, substantially little or nosurface defects, and a crystal defect density of about 5×10⁶/cm² orless.

A yet further aspect of the present invention relates to aheterostructure which includes at least the above-mentioned substratematerial. Specifically, the heterostructure of the present inventioncomprises a Si-containing substrate; an insulating region that isresistant to Ge diffusion present atop the Si-containing substrate; asubstantially relaxed SiGe layer present atop the insulating region,wherein the substantially relaxed SiGe layer has a thickness of about2000 nm or less, a measured relaxation value of about 50% or greater,substantially little or no surface defects, and a crystal defect densityof about 5×10⁶/cm² or less; and a strained Si layer formed atop thesubstantially relaxed SiGe layer.

Other aspects of the present invention relate to superlattice structuresas well as templates for other lattice mismatched structures whichinclude at least the SiGe-on-insulator substrate material of the presentinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A-1F are pictorial representations (through cross-sectionalviews) showing the basic processing steps of a first embodiment of thepresent invention which is used in fabricating a highly-relaxed,low-defect SGOI substrate material.

FIGS. 2A-2B are pictorial representations (through cross-sectionalviews) showing an alternative embodiment of the present inventionwherein a Si cap layer is formed atop a SiGe alloy layer which ispresent on an unpatterned (1A) or patterned (1B) substrate.

FIGS. 3A-3F are pictorial representations (through cross-sectionalviews) showing the basic processing steps of a second embodiment of thepresent invention which is used in fabricating a highly-relaxed,low-defect SGOI substrate material.

FIG. 4 is a structure that can be formed using the inventive SGOIsubstrate material.

FIGS. 5A-5C are pictorial representations (through cross sectionalviews) showing the basic processing steps of a third embodiment of thepresent invention which is used in fabricating a highly-relaxed,low-defect SGOI substrate material.

DETAILED DESCRIPTION OF THE INVENTION

The present invention, which provides methods of fabricating improvedthin, high-quality, highly-relaxed SiGe-on-insulator substrate materialswhich can then serve as a lattice mismatched template for subsequentovergrowth of epitaxial Si, will now be described in greater detail byreferring to the drawings that accompany the present application. It isnoted that in the accompanying drawings like and/or correspondingelements are referred to by like reference numerals.

Reference is first made to FIG. 1A and FIG. 1B which show two differenttypes of initial substrate materials that can be employed in the presentinvention. Specifically, the initial substrate materials illustrated inFIGS. 1A-1B comprise Si-containing semiconductor substrate 10, barrierlayer 12 which is resistant to Ge diffusion (hereinafter “barrierlayer”) present atop a surface of Si-containing semiconductor substrate10 and first single crystal Si layer 14 having misfit and TD densitiesof less than about 1×10⁵ defects/cm² present atop the barrier layer. Thedifference between the two initial structures depicted in the drawingsis that, in FIG. 1A, the barrier layer is present continuouslythroughout the entire structure, whereas in FIG. 1B, the barrier layeris present as discrete and isolated regions or islands that aresurrounded by semiconductor material, i.e., layers 10 and 14. Note thatthe initial structure shown in FIG. 1A thus includes an unpatternedbarrier layer, whereas the initial structure of FIG. 1B includes apatterned barrier layer.

Notwithstanding whether the barrier layer is patterned or unpatterned,the initial structure may be a conventional silicon-on-insulator (SOI)substrate material wherein region 12 is a buried oxide (BOX) regionwhich electrically isolates first single crystal Si layer 14 fromSi-containing semiconductor substrate 10. The term “Si-containing” asused herein denotes a semiconductor substrate that includes at leastsilicon. Illustrative examples include, but are not limited to: Si,SiGe, SiC, SiGeC, Si/Si, Si/SiC, Si/SiGeC, and preformedsilicon-on-insulators which may include any number of buried oxide(continuous, non-continuous or mixtures of continuous andnon-continuous) regions present therein.

The SOI substrate may be formed utilizing conventional SIMOX (separationby ion implantation of oxygen) processes well-known to those skilled inthe art, as well as the various SIMOX processes mentioned in co-assignedU.S. patent applications Ser. Nos. 09/861,593, filed May 21, 2001;09/861,594, filed May 21, 2001; 09/861,590, filed May 21, 2001;09/861,596, filed May 21, 2001; and 09/884,670, filed Jun. 19, 2001 aswell as U.S. Pat. No. 5,930,634 to Sadana, et al., the entire contentsof each are incorporated herein by reference. Note that the processdisclosed in the '590 application can be employed herein to fabricatethe patterned substrate shown in FIG. 1B.

Alternatively, the SOI substrate material may be made using otherconventional processes including, for example, a thermal bonding andcutting process.

In addition to SOI substrates, the initial substrates shown in FIGS. 1Aand 1B may be a non-SOI substrate which is made using conventionaldeposition processes as well as lithography and etching (employed whenfabricating a patterned substrate). Specifically, when non-SOIsubstrates are employed, the initial structure is formed by depositing aGe diffusion barrier layer atop a surface of a Si-containing substrate,via conventional deposition or thermal growing processes, optionallypatterning the barrier layer by employing conventional lithography andetching; and thereafter forming a single crystal Si layer atop thebarrier layer using conventional deposition processes including, forexample, chemical vapor deposition (CVD), plasma-assisted CVD,sputtering, evaporation, chemical solution deposition or epitaxial Sigrowth.

Barrier layer 12 of the initial structure shown in FIGS. 1A and 1Bcomprises any insulating material which is highly resistant to Gediffusion. Examples of such insulating and Ge diffusion resistantmaterials include, but are not limited to: crystalline ornon-crystalline oxides or nitrides.

The thickness of the various layers of the initial structure may varydepending on the process used in making the same. Typically, however,single crystal Si layer 14 has a thickness of from about 1 to about 2000nm, with a thickness of from about 10 to about 200 nm being more highlypreferred. In the case of barrier layer 12 (i.e., Ge diffusion resistantlayer), that layer may have a thickness of from about 1 to about 1000nm, with a thickness of from about 20 to about 200 nm being more highlypreferred. The thickness of the Si-containing substrate layer, i.e.,layer 10, is inconsequential to the present invention. It is noted thatthe thicknesses provided above are exemplary and by no ways limit thescope of the present invention.

For simplicity, the remaining steps of the present invention will makeuse of the initial structure shown in FIG. 1A. The remaining stepshowever work well with the initial structure shown in FIG. 1B.

FIG. 1C illustrates the structure that is formed after Si_(x)Ge_(1-x)layer 16 (wherein x is 0 or a number less than 1) is formed atop firstsingle crystal Si layer 14. The “Si_(x)Ge_(1-x)” layer is hereinafterreferred to as a SiGe alloy layer. The SiGe alloy layer of the presentinvention may comprise SiGe alloys having up to 99.99 atomic percent Ge(when x is less than 1), as well as pure Ge (when x=0) that comprise 100atomic percent Ge. In one embodiment of the present invention, it ispreferred that the Ge content in the SiGe alloy layer be from about 0.1to about 99.9 atomic percent, with a Ge atomic percent of from about 10to about 35 being even more highly preferred. In the drawings, referencenumeral 13 denotes the interface between barrier layer 12 and singlecrystal Si layer 14.

In accordance with the present invention, the SiGe alloy is formed atopfirst single crystal Si layer 14 using a conventional epitaxial growthmethod that is well-known to those skilled in the art which is capableof (i) growing a thermodynamically stable (below a critical thickness)SiGe alloy, or (ii) growing a SiGe alloy layer that is metastable andfree from defects, i.e., misfit and TD dislocations. Illustrativeexamples of such epitaxial growing processes that are capable of satisfyconditions (i) or (ii) include, but are not limited to: low-pressurechemical vapor deposition (LPCVD), ultra-high vacuum chemical vapordeposition (UHVCVD), atmospheric pressure chemical vapor deposition(APCVD), molecular beam epitaxy (MBE) and plasma-enhanced chemical vapordeposition (PECVD).

The thickness of the SiGe alloy layer formed at this point of thepresent invention may vary, but typically layer 16 has a thickness offrom about 10 to about 500 nm, with a thickness of from about 20 toabout 200 nm being more highly preferred.

In one alternative embodiment of the present invention, see FIGS. 2A-2B,optional cap layer 18 is formed atop SiGe alloy layer 16 prior toperforming the heating step of the present invention. The optional caplayer employed in the present invention comprises any Si materialincluding, but not limited to: epitaxial silicon (epi-Si), amorphoussilicon (a:Si), single or polycrystalline Si or any combination thereofincluding multilayers. In a preferred embodiment, the cap layer iscomprised of epi Si. It is noted that layers 16 and 18 may, or may not,be formed in the same reaction chamber.

When present, optional cap layer 18 has a thickness of from about 1 toabout 100 nm, with a thickness of from about 1 to about 30 nm being morehighly preferred. The optional cap layer is formed utilizing anywell-known deposition process including the epitaxial growth processesmentioned above.

In one embodiment of the present invention, it is preferred to form aSiGe alloy (15 to 20 atomic percent Ge) layer having a thickness of fromabout 1 to about 200 nm on the surface of a single crystal Si layer, andthereafter forming a Si cap layer having a thickness of from about 1 toabout 100 nm atop the SiGe alloy layer.

Next, the structure, with or without the optional Si cap layer, is thenpatterned so as to provide the structure illustrated in FIG. 1D.Specifically, the structure, with or without the optional Si cap layer,is patterned by using conventional lithography and etching. Thelithography step includes applying a photoresist (not shown) to thesurface of the structure, either atop the SiGe alloy layer or theoptional Si cap layer, exposing the photoresist to a pattern ofradiation, and developing the pattern into the photoresist by utilizinga conventional resist developer. Note that the patterned photoresistprotects portions of the structure, while leaving other portions of thestructure exposed. With the patterned photoresist in place, the exposedportions of the structure are then etched stopping atop barrier layer12. In some embodiments, the etching step thus removes exposed portionsof the SiGe alloy layer as well as the single crystal Si layerunderlying the exposed portions of the SiGe alloy, while in otherembodiments, the optional Si cap is first etched and thereafter theunderlying SiGe alloy and single crystal Si layers may be removed.

The etching step may be carried out using a single etching step, ormultiple etching steps may be employed in forming the structure shown,for example, in FIG. 1D. Notwithstanding whether a single- or multiple-etching process is performed, etching may be performed using aconventional dry etching process such as, reactive-ion etching, plasmaetching, ion beam etching, laser ablation or any combination thereof. Inaddition to dry etching, the present invention also contemplates thatthis etching step may include the use of a wet chemical etching processor a combination of wet etching and dry etching may be performed. Whenwet chemical etching is utilized, a chemical etching that is highlyselective in removing Si as compared to oxide or nitride is employed.Following etching the patterned photoresist is removed at this point ofthe inventive process utilizing a conventional resist stripping process.

The patterned layers of SiGe layer 16, Si layer 14 and, if present,optional Si cap layer 18 are referred to herein as an island. It isnoted that although the drawings depict the formation of a single islandstructure, the present invention also contemplates the formation of amultitude of such island structures on the surface of barrier layer 12.The islands are generally small in size, having a lateral width of about500 μm or less. More preferably, the patterned islands have a lateralwidth of from about 0.01 to about 100 μm. It should be noted that thewidth of the islands formed by the present invention must be sufficientto permit relaxation of the SiGe film by ensuring that the forces ofrelaxation in the island regions outweigh the forces that opposerelaxation.

In some embodiments, the optional Si cap layer may be formed atop thepatterned surface of SiGe alloy layer 16 at this point of the presentinvention. This embodiment of the present invention is not specificallyillustrated in the present invention.

The patterned structure containing the above-mentioned islands is thenheated, i.e., annealed, at a temperature which permits relaxation of thestrained SiGe alloy layer and subsequent interdiffusion of Ge throughoutfirst single crystal Si layer 14, SiGe alloy layer 16 and, if present,the optional Si cap thereby forming substantially relaxed, singlecrystal SiGe layer 20 atop the barrier layer (See FIG. 1E). Therelaxation anneal may be performed separately from the interdiffusionanneal or combined in one annealing process. The heating can beperformed in a tube furnace or using rapid-thermal annealing (RTA)tools. Note that oxide layer 22 is formed atop layer 20 during theheating step. This oxide layer is typically, but not always, removedfrom the structure after the heating step using a conventional wet etchprocess wherein a chemical etchant such as HF that has a highselectivity for removing oxide as compared to SiGe is employed.Alternatively, this oxide layer may be removed using a conventional dryetching process such as reactive-ion etching.

Note that when the oxide layer is removed, a second single crystal Silayer can be formed atop layer 20 and the above processing steps of thepresent invention may be repeated any number of times to produce amultilayered relaxed SiGe substrate material.

The oxide layer formed after the heating step of the present inventionhas a variable thickness which may range from about 2 to about 2000 nm,with a thickness of from about 2 to about 500 nm being more highlypreferred.

Specifically, the heating step of the present invention is an annealingstep which is performed at a temperature of from about 900° to about1350° C., with a temperature of from about 1200° to about 1335° C. beingmore highly preferred. Moreover, the heating step of the presentinvention can be carried out in an oxidizing ambient which may includeat least one oxygen-containing gas such as O₂, NO, N₂O, H₂O (steam),ozone, air and other like oxygen-containing gases. The oxygen-containinggas may be admixed with each other (such as an admixture of O₂ and NO),or the gas may be diluted with an inert gas such as He, Ar, N₂, Xe, Kr,or Ne.

The heating step may be carried out for a variable period of time whichtypically ranges from about 10 to about 1800 minutes, with a time periodof from about 60 to about 600 minutes being more highly preferred. Theheating step may be carried out at a single targeted temperature, orvarious ramp and soak cycles using various ramp rates and soak times canbe employed.

The heating step can be performed under an oxidizing ambient to achievethe presence of a surface oxide layer, i.e., layer 22, which acts as adiffusion barrier to Ge atoms. Therefore, once the oxide layer is formedon the surface of the structure, Ge becomes trapped between barrierlayer 12 and oxide layer 22. As the surface oxide increases inthickness, the Ge becomes more uniformly distributed throughout layers14, 16, and optionally 18, but it is continually and efficientlyrejected from the encroaching oxide layer. So as the (now homogenized)layers are thinned during this heating step, the relative Ge fractionincreases. Efficient thermal mixing is achieved in the present inventionwhen the heating step is carried out at a temperature of from about1200° to about 1320° C. in a diluted oxygen-containing gas.

It is also contemplated herein to use a tailored heat cycle which isbased upon the melting point of the SiGe alloy layer. In such aninstance, the temperature is adjusted to tract below the melting pointof the SiGe alloy layer.

Note that if the oxidation occurs too rapidly, Ge cannot diffuse awayfrom the surface oxide/SiGe interface fast enough and is eithertransported through the oxide (and lost) or the interfacialconcentration of Ge becomes so high that the alloy melting temperaturewill be reached.

The role of the heating step of the present invention is (1) to allow Geatoms to diffuse more quickly thereby maintaining a homogeneousdistribution during annealing; and (2) to subject the (‘initially’)strained layer structure to a thermal budget which will facilitate anequilibrium configuration. After this heating step has been performed,the structure includes a uniform and substantially relaxed SiGe alloylayer, i.e., layer 20, sandwiched between barrier layer 12 and surfaceoxide layer 22.

The heating step can also be performed in a non-oxidizing ambient. Inthis case, the anneal would simply homogenize the Ge throughout thefirst single crystal Si and the SiGe layers. This would be preferred inthe situation where the lateral dimensions patterned islands were verysmall and oxidation of the structure might consume the island by lateraloxidation of the sidewalls.

In accordance with the present invention, substantially relaxed SiGelayer 20 has a thickness of about 2000 nm or less, with a thickness offrom about 10 to about 200 nm being more highly preferred. Note that thesubstantially relaxed SiGe layer formed in the present invention isthinner than prior art SiGe buffer layers and has a defect densityincluding misfits and TDs, of about 5×10⁶ defects/cm² or less.

The substantially relaxed SiGe layer formed in the present invention hasa final Ge content of from about 0.1 to about 99.9 atomic percent, withan atomic percent of Ge of from about 10 to about 35 being more highlypreferred. Another characteristic feature of substantially relaxed SiGelayer 20 is that it has a measured lattice relaxation of from about 50%or greater, with a measured lattice relaxation of from about 75 to about100% being more typically preferred. It is noted that 100% relaxation ismost preferred in the present invention.

As stated above, surface oxide layer 22 may be stripped at this point ofthe present invention so as to provide the SiGe-on-insulator substratematerial shown, for example, in FIG. 1F.

The above discussion, with illustration to FIGS. 1A-1F, arerepresentative of the first embodiment of the present invention. Thesecond embodiment, which includes a partial relaxation heating stepprior to patterning will be now described in more detail, with referenceto FIGS. 3A-3F.

FIG. 3A shows an initial structure (including Ge barrier layer 12sandwiched between single crystal Si layer 14 and Si-containingsubstrate 10) that is employed in the second embodiment of the presentinvention. Note that the structure shown in FIG. 3A is identical to thatshown in FIG. 1A. In addition to utilizing this specific initialstructure, the structure illustrated in FIG. 1B may also be employed.

Next, SiGe alloy layer 16 is formed atop first single crystal Si layer14 using the processing steps mentioned above so as to provide thestructure shown in FIG. 3B. At this point of the inventive process,optional Si cap layer 18 may be formed atop the SiGe alloy layer andthereafter the structure, with or without the optional Si cap layer, issubjected to a first heating step which is performed at a temperaturewhich permits interdiffusion of Ge throughout the first single crystalSi layer and the Si_(x)Ge_(1-x) layer to form either partially relaxedor fully-strained, single crystal SiGe layer 19 atop barrier layer 12.The first heating step of the present invention is carried out at atemperature of from about 900° to about 1335° C., with a temperature offrom about 1150° to about 1320° C. being more highly preferred.

Moreover, the first heating step of the present invention is carried outin an oxidizing ambient which includes at least one oxygen-containinggas such as O₂, NO, N₂O, H₂O (steam), ozone, air and other likeoxygen-containing gases. The oxygen-containing gas may be admixed witheach other (such as an admixture of O₂ and NO), or the gas may bediluted with an inert gas such as He, Ar, N₂, Xe, Kr, or Ne. The firstheating step may be carried out for a variable period of time whichtypically ranges from about 10 to about 1800 minutes, with a time periodof from about 60 to about 600 minutes being more highly preferred. Thefirst heating step may be carried out at a single targeted temperature,or various ramp and soak cycles using various ramp rates and soak timescan be employed.

The structure formed after the first heating step is shown, for example,in FIG. 3C. Note that the first heat step forms either partially relaxedor fully-strained SiGe layer 19 atop the surface of barrier layer 12. Itis also noted that a thin oxide layer typically begins to form atop thepartially relaxed SiGe layer at this point of the present invention. Forclarity, however, this thin oxide layer has be omitted from thedrawings.

Next, SiGe layer 19 is then patterned as discussed to provide thepatterned structure shown in FIG. 3D. The SiGe islands formed have thesame lateral width as mentioned above. After patterning, the structureshown in FIG. 3D is then subjected to a second heating step that iscarried out at a temperature which permits further relaxation of thesingle crystal SiGe layer to form substantially relaxed, single crystalSiGe layer 20 atop a portion of the barrier layer, See FIG. 3E. Note thepresence of oxide layer 22 atop the relaxed SiGe layer. The thickness ofoxide layer 22 may be very thin (sub-nanometer) or thicker depending onthe annealing ambient and temperature.

The second heating step of the present invention is carried out at atemperature of from about 900° to about 1335° C., with a temperature offrom about 1150° to about 1320° C. being more highly preferred.Moreover, the second heating step of the present invention may becarried out in an oxidizing ambient which includes at least oneoxygen-containing gas such as O₂, NO, N₂O, H₂O (steam), ozone, air andother like oxygen-containing gases. The oxygen-containing gas may beadmixed with each other (such as an admixture of O₂ and NO), or the gasmay be diluted with an inert gas such as He, Ar, N₂, Xe, Kr, or Ne. Thesecond heating step may also be carried out in a non-oxidizing ambientas well to minimize the consumption and distortion of the patternedislands. The second heating step may be carried out for a variableperiod of time which typically ranges from about 1 to about 1800minutes, with a time period of from about 10 to about 600 minutes beingmore highly preferred. The second heating step may be carried out at asingle targeted temperature, or various ramp and soak cycles usingvarious ramp rates and soak times can be employed.

FIG. 4 shows the structure that is obtained after forming Si layer 24atop the SiGe layer of FIGS. 1F or 3F. Specifically, Si layer 24 isformed using a selective epitaxial deposition process well-known in theart. The thickness of epi-Si layer 24 may vary, but typically, epi-Silayer 24 has a thickness of from about 1 to about 100 nm, with athickness of from about 1 to about 30 nm being more highly preferred.

FIGS. 5A-5C show a third method of the present invention. In the thirdmethod, first single crystal Si layer 14 of an SOI wafer (alsocontaining Ge barrier layer 12 and semiconductor substrate 10) ispatterned via conventional lithography and etching to provide astructure containing a predetermined geometric shape as is shown, forexample, in FIG. 5A. After patterning, epitaxial SiGe is selectivelygrown at a temperature which is sufficiently high enough to causein-situ relaxation of the SiGe layer forming substantially relaxed SiGeregion 20. See FIG. 5B

The in-situ relaxation occurs utilizing a selective deposition processsuch as CVD wherein the temperature of deposition is about 600° C. orgreater. Preferably, the in-situ relaxation occurs at a temperature offrom about 800° to about 1100° C.

Note that SiGe region 20 has substantially the same geometric shape aspatterned single crystal Si layer 14. FIG. 5C shows Si layer 24 beingformed on the structure shown in FIG. 5B.

In some instances, additional SiGe can be formed atop relaxed SiGe layer20 utilizing the above mentioned processing steps, and thereafter epi-Silayer 24 may be formed. Because layer 20 has a large in-plane latticeparameter as compared to epi-layer 24, epi-layer 24 will be strained ina tensile manner.

In either the first, second or third embodiment described above, boronor another like impurity ion may be implanted into the Ge barrier layerprior to heating the structure using a conventional ion implantationprocess well-known to those skilled in the art. The impurity ions areemployed in the present invention to lower the temperature at whichelastic relaxation can occur. Specifically, the implantation of impurityions into the Ge barrier layer can lower the relaxation temperature asmuch as 300° C. or greater.

In either the first, second, or third embodiment described above,hydrogen ions can be implanted in such a way as to place the peak of theimplanted ion distribution at or near the buried oxide/top Si interface.This can enhance the relaxation of the SiGe layer and can be used inconjunction with the patterning methods described here. The hydrogen ionimplantation can be performed using the techniques and conditionsdisclosed in co-assigned U.S. application Ser. No. 10/196,611, filedJul. 16, 2002, the entire content of which is incorporated herein byreference. In place of hydrogen, deuterium, helium, oxygen, neon andother like ions that are capable of forming defects that allowmechanical decoupling at or near the first single crystal Si/barrierlayer interface can be employed. Mixtures of the above-mentioned ionsare also contemplated herein. Preferred ions include hydrogen ions, andpreferred conditions include: an ion concentration of below 3E16atoms/cm² and an implant energy of from about 1 to about 100 keV. Theions can be implanted before or after patterning on any of the threeembodiments mentioned above.

As stated above, the present invention also contemplates superlatticestructures as well as lattice mismatched structures which include atleast the SiGe-on-insulator substrate material of the present invention.In the case of superlattice structures, such structures would include atleast the substantially relaxed SiGe-on-insulator substrate material ofthe present invention, and alternating layers of Si and SiGe formed atopthe substantially relaxed SiGe layer of the substrate material.

In the case of lattice mismatched structures, GaAs, GaP or other likeIII/V compound semiconductors would be formed atop the substantiallyrelaxed SiGe layer of the inventive SiGe-on-insulator substratematerial.

The following example is provided to illustrate some of the advantagesof the present invention over a conventional thermal mixing process.

EXAMPLE

An initial structure of 350 Å SIMOX SOI with a deposited epitaxial layerof 300 Å Si_(0.8)Ge_(0.2) followed by a 200 Å Si “Cap” layer wasthermally mixed at high temperatures (from 1200° to 1320° C.) and the(continuous) films were found not to relax. In other words, even thoughthe Ge had been mixed throughout the layers, and concentrated by theprocess of oxidation, the SiGe film over the oxide had retained thein-plane lattice parameter of bulk Si. The elastic strain energy withinthis layer was below that required to relax plastically, i.e., by theformation of strain-relieving defects, and thus no relaxation occurredat all.

The same initial structure was used and patterned by removing regions ofthe original Si/SiGe/SOI film prior to heating thereby delineatingislands of film. The size of the patterned islands varied from a fewtenths to hundreds of microns on edge. The same heating procedure wascarried out and the patterned structure was measured to be 87% relaxedas measured by X-ray diffraction (large beam size averaging over manyfeature sizes). Further investigation of individual structures usingPlan-View Transmission Electron Microscopy (PV-TEM) (using Moireanalysis) showed that islands up to about 10 μm on edge relaxedcompletely (100%), whereas larger structures relaxed partially orasymmetrically, depending on the size and shape of the island.

Another important feature of the elastic relaxation of SiGe islandsusing this procedure is the total absence of defects as measured byPV-TEM. No defects at all were found after scanning and sets the upperlimit of defects at <1×10⁵ cm⁻². X-Ray analysis on thicker starting SiGelayers (600 Å-17% SiGe on 350 Å SIMOX SOI) showed 99% relaxation,indicating that thicker films indeed relax more.

While the present invention has been particularly shown and describedwith respect to preferred embodiments thereof, it will be understood bythose skilled in the art that the foregoing and other changes in formsand details may be made without departing from the spirit and scope ofthe present invention. It is therefore intended that the presentinvention not be limited to the exact forms and details described andillustrated, but fall within the scope of the appended claims.

1. A method of forming a substantially relaxed, low-defect SGOIsubstrate material comprising the steps of: forming a Si_(x)Ge_(1-x)layer,wherein x=0 or a number less than 1, on a surface of a firstsingle crystal Si layer, said first single crystal Si layer has aninterface with an underlying barrier layer that is resistant to Gediffusion; patterning said Si_(x)Ge_(1-x) layer and said first singlecrystal Si layer to provide a patterned structure comprising at leastone island of said Si_(x)Ge_(1-x) layer and said Si layer on a surfaceof said barrier layer, said at least one island having bare verticalsidewalls and a relaxation force that is greater than forces that opposerelaxation; and heating said patterned structure having said barevertical sidewalls at a temperature which permits relaxation of strainwithin the patterned layers and subsequent interdiffusion of Gethroughout the patterned first single crystal Si layer and the patternedSi_(x)Ge_(1-x) layer to form a substantially relaxed, single crystalSiGe layer atop a portion of the barrier layer.
 2. The method of claim 1wherein said barrier layer is a patterned barrier layer.
 3. The methodof claim 1 wherein said barrier layer is an unpatterned barrier layer.4. The method of claim 1 wherein said barrier layer comprises impurityions incorporated therein.
 5. The method of claim 1 wherein saidSi_(x)Ge_(1-x) layer is formed by an epitaxial growth process selectedfrom the group consisting of low-pressure chemical vapor deposition,atmospheric pressure chemical vapor deposition, ultra-high vacuumchemical vapor deposition, molecular beam epitaxy, plasma-enhancedchemical vapor deposition, and ion-assisted deposition.
 6. The method ofclaim 1 further comprising forming a Si cap layer atop saidSi_(x)Ge_(1-x) layer prior to performing the heating step.
 7. The methodof claim 6 wherein said Si cap layer comprises epi-Si, a:Si, single orpolycrystalline Si or any combination and multilayer thereof.
 8. Themethod of claim 1 wherein said patterning includes lithography andetching.
 9. The method of claim 1 wherein a surface oxide layer formsduring said heating step.
 10. The method of claim 9 further comprisingremoving said surface oxide layer utilizing a wet chemical etch processor dry etching.
 11. The method of claim 1 wherein said heating iscarried out in an oxidizing ambient which comprises at least oneoxygen-containing gas.
 12. The method of claim 11 wherein said at leastone oxygen-containing gas comprises O₂, NO, N₂O, steam, ozone, air ormixtures thereof.
 13. The method of claim 11 further comprising an inertgas, said inert gas being employed to dilute said at least oneoxygen-containing gas.
 14. The method of claim 1 wherein said heating iscarried out in a non-oxidizing ambient which comprises any of the inertgases or mixtures thereonf.
 15. The method of claim 1 wherein saidheating is performed at a temperature of from about 900° to about 1350°C.
 16. The method of claim 15 wherein said heating is performed at atemperature of horn about 1200° to about 1335° C.
 17. The method ofclaim 1 further comprising growing an additional SiGe layer atop saidsubstantially relaxed SiGe layer.
 18. The method of claim 17 furthercomprising forming a strained Si layer atop said additional SiGe layer.19. The method of claim 1 further comprising forming a strained Si layeratop said substantially relaxed SiGe layer.
 20. The method of claim 1wherein ions that are capable of forming defects that allow mechanicaldecoupling at or near said interface are implanted into saidSi_(x)Ge_(1-x) layer either before or after said patterning.
 21. Themethod of claim 20 wherein said implanting ions comprise hydrogen,deuterium, helium, oxygen, neon or mixtures thereof.
 22. The method ofclaim 21 wherein implanting ions are hydrogen ions.